The ingredients that absorb UV light and prevent it from reaching your skin can change or degrade with time and extreme temperature, diminishing the effectiveness of the sunscreen, said Dr. John Bailey, chief scientist with the Personal Care Products Council. If the product still looks, smells and feels right, you can probably use it for a year past the expiration if you're willing to take the risk (that is, if you tolerate the sun well), Bailey said. But if you're fair-skinned or burn easily, it's best to abide by the date. Other doctors, such as Glogau, advise people to buy a new bottle each year.